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Related topics

The KickDrill app covers the topics taught in the WellControl school. In addition, other topics are also covered but is not part of the exams. An example of this is Kick Tolerance where a case scenario is calculated through. The below shows a method that can be used to find how much gas you can take in without fracturing the weak spot in the well.

 

Example: We have the following input:

  • TVD TD: 3800 m
  • TVD Shoe (or Weak spot): 2950 m
  • MW: 1.50 sg
  • LOT@shoe: 1.76 sg
  • Max Potential Pore Pressure: 1.65 sg
  • Kick density: 0.22 sg
  • Cap BHA/OH: 43.6 l/m
  • Cap DP/OH: 63,4 l/m
  • Length of BHA: 190 m
  • We for simplicity we assume a vertical well

1: Estimating Kick Intensity
Decide what is your maximum expected pore-pressure for the section (ie.. in ppg or g/cc) and subtract the mud-weight (expected to be) in use at that point. This is referred to as the “Kick intensity”. For added  safety a safety factor can also be added to the estimated max expected PP.
Using the input from above: We estimated max PP to be 1.65 sg and Mud Weight in use while entering the zone to be 1.50 sg: Intensity: 1.65-1.50=0.15 sg

2: Find MAASP
Find the MAASP using the Mudweight from above and the current LOT, expressed in pressure (Psi or BAR):

1.76 – 1.50 x 2950 x 0.0981= 75.3 Bar

3: Find max INFLUX Height
Find the Influx height by subtracting the Kick Intensity at TD expressed as pressure from the MAASP, and divide this with the MW minus the Gas Gradient, expressed in pressure per depth (eg. Bar/m). Note: Remember to use Vertical depth.

(75.3 -((1.65-1.5)x3800x0.0981))/((1.50-0.22)x0.0981)=153.9m

This is the maximum height of mudcolumn we can loose and replace with Gas with the assumptions made above.

4: Find Kick Volume 1 @ TD
Take the result from (3), and find how much volume this height of influx represents at TD. Remember to compensate for MD versus TD if the well is deviated (TVD=cosine to the well inclination x Measured depth).

At TD, the volume between the Open hole and BHA is 43.3 l/m in volume; since we have 190 m of BHA with this volume-displacement and the height found in (3) was 153.9 m, we can use the full length with this volume (not overshooting to also needing to use DP displacement). We assume a vertical well.

153.9m x 43.3 l/m= 6664 l

This is KICK VOLUME 1 @ TD.

5: Volume at shoe w maximum height:

Transfer the kick column height (153.9 m) up to below the casing shoe, find new volume using 63.4 l/m. If the well was not vertical, we would need to compensate for MD versus TD.

153.9m x 63.4 l/m= 9757 l

This is the “Reference volume” we will use to find Volume 2

6: What was this volume when entering the well?

We then need to calculate what this reference (gas-volume) found in (5) was when it initially entered the well at the kick zone and at the higher pressure (we use here @ TD). We then use Boyles law where P1xV1 = P2 x V2, where P is pressure and V is volume. We set P1 and V1 to be at the shoe. P1= LOT pressure @ shoe, V1 = “Reference” Volume at max height (see pt.3) found in (5). P2 = The Maximum pore-pressure we estimated in (1). As we now have P1, V1, and P2 we can find V2.

1.76x2950x0.0981) (P1) x 9757 (V1) / (1.65x3800x0.0981) (P2)  = 8079 l = V2

This 8079 liter of gas will increase to 9757 when at the shoe. However, the volume found in (4) 6664 liter will be the designing volume as this is the maximum volume we can have at TD without exceeding our maximum vertical column of gas in the well. If we had taken in a gascolumn of 8079 liter, it would have occupied more than 159 meter of vertical height when at TD and around the BHA.

Note: This assuming out input data is according to our estimates.